In a variety of fields, there is a growing need for utilizing miniature camera modules of high quality. Such a camera module includes an image sensor and a fixed focus lens structure.
Lens structures for optical devices such as digital cameras consist of multiple lens elements assembled in a single barrel or stacked in wafer form utilizing spacers, to create fixed focus lens structures. Such fixed focus lens structures have a fixed focal plane. A focus-free camera module refers to a camera module that is constructed utilizing a camera housing with lenses integrated into the housing permanently with respect to the image sensor substrate. Images between infinity and some close distance to the camera are focused on the image plane of the image sensor.
Camera module assembly includes mounting the lens structure with respect to the image sensor. Best manufacturing tolerances are such that allowable assembly variations cause focus plane misalignment to such an extent that the focus plane does not fall correctly on the image plane of the image sensor in some cases not adequately so. These are not physical defects but rather shortcomings of the manufacturing process. Such assembly errors and optical errors cause the camera module to experience distortions and aberrations. Typically, assembly of such a camera module therefore leaves the camera module out of focus. In the prior art, a focus offset is provided by adjustment screws or adjustment structures. Unfortunately use of such mechanical adjustment complicates manufacturing by necessitating such additional camera module components and introduces manufacturing overheads by requiring time intensive manipulation of individual miniature components to mechanically move the lens structure to focus on objects at varying distances from the camera system. Moreover, the adjustment structure undesirably adds bulk to a camera module for what is essentially a single use.
There is a general need to increase manufacturing yields and to minimize the impact of manufacturing defects.